The present invention relates to a plastic trellis stake for rows of tensioned wires for supporting tendrils and twigs of plants, more particularly, grape vines in vineyards.
The invention in another aspect also relates to a wire support to be used in connection with such a trellis stake, a support member for the wire being part of a fastening clamp to be disposed around a trellis stake.
The dressing of grape vines in vineyards is very labourious and for this reason instead of separately fastening the grape vine to a single stake, grape vines are fastened in rows along tensioned wires. With respect to mechanisation in vine dressing in vineyards, wires in a trellis have to be very accurately tensioned. For this reason the trellis stakes for supporting the wires have to be very accurately lined out.
Given an amount of about 5000 grape vines pro hectare for farming the ground and to facilitate gathering the grapes, the trunks of grape vines are to be guided upwardly towards a lower tensioned wire which generally is called the bending wire. Depending on the way of guiding the tendrils, a second bending wire can be situated above the first one while furthermore a double fastening wire is used, mostly followed by two or three single fastening wires, until a trellis height is obtained of about 1.80 m.
In modern vineyards the plots generally have a maximum wire length between 50 to 60 meters their mutual position depending on the kind of grape vine and the way in which the tendrils are to be guided. It is therefore necessary that the level of the wires can be adjusted along the stake.
Considering the life time of the vineyard and the possible exhaustion of the ground, the age of a grape vine is about 20 years before the quality of the grapes and the yields will decrease. This means that a trellis stake has to last about 20 years, although a multiple of said amount is preferred. A good alignment of the trellis stake and straight trunks of the grape vines are especially of importance with respect to a mechanical gathering of grapes, although such a mechanical gathering of grapes was hitherto not entirely satisfactory.
By arranging vineyards in the way as described above a reduction of more than 50% of the costs of dressing the grape vines is obtained. Regarding the number of trellis stakes it should be noted that in one trellis the distance between the stakes is about 4 to 5 meters. For mechanisation the space between the rows of trellis stakes is increased, the spaces then being about 2 to 2.80 m. wide. In addition a great sturdiness of the stake is necessary in view of gales and possible squalls, especially when the tendrils are in full foliage.
In practice very often wooden trellis stakes are used which stakes have been impregnated in order to prevent wood rot. Wooden stakes are very easy to handle and the wires can be simply fastened to the stakes by means of clamps or eyes. Plastic hooks fastened to the stake by a nail, are also often used. The advantage of such hooks is that the double fastening wires, during growing of the foliage and new tendrils, can be easily hooked out and hooked in again, while enclosing the foliage, so protecting fresh tendrils against winds and avoiding their being pressed aside and getting drooped. However, wooden stakes are not fully weather-proof and during a period of, f.i., 20 years it often happens that such stakes rot near the ground, causing the trellis stake to get out of line by winds or even to get broken.
Trellis stakes made of pre-stressed concrete are also known in the art. These stakes comprise at either side rows of grooves into which grooves plastic eyes are inserted for supporting the wires. Trellis stakes of concrete, however, are very heavy and difficult to handle and frost can affect the quality of the concrete, while the stake can even be broken by frozen water accumulated in a crack or groove in the stake.
Steel trellis stakes are also known in the art, having a C-shaped cross-section, with hooks punched out at the opposing sides of the stake. These stakes are made corrosion-proof by galvanisation. It often happens, however, that said galvanisation is damaged by tools, particularly at end stakes, with the result that the stakes yet become rusty and a long life of 20 years cannot possibly be obtained.
In practice efforts have been made to make plastic stakes, but up till now these are unseccessful as plastic stakes generally are too weak, unless the stake diameter is large. As the number of stakes compared with the number of grape vines pro hectare is considerably high, increasing the stake diameter is disadvantageous with respect to causing shadows. During the month of September, so just before gathering the grapes of the late kind, each day of sunlight increases the amount of sugar in one grape by 1.degree. Oechsele (0.3.degree. Briggs). This means that shadows caused by stakes result in wines from grapes of which the quality is considered to be slightly inferior to that obtained in normal cases (i.e. in the absence of shadows).
Trellis stakes made of tubular plastic material are also known, as well as a plastic wire support material which is to be fastened around the tubular stake. To avoid shadows caused by the stake(s) it has been tried to make rigid plastic stakes having a profiled cross-sectional shape, e.g. a T-shaped cross-section. However, wire supports are to be slid around a stake and have to be fastened in the correct position. It is therefore a drawback of the latter stakes that a wire support can be damaged, as a result of the yearly trimming which is mostly performed with pneumatically driven pruning-shears. As a consequence wire supports situated thereabove have to be moved to a lower position and a new wire support for the uppermost wire is to be supplied, which is very time-consuming. In case a wire is cut through by a pruning shear, this is less disadvantageous, because the wire can easily be connected again by an intermediate part of wire.